JPH10282759A - Image-on-image multicolor printing device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a bias voltage applied in an image forming process and (or) a developing process and to prevent overplating, that is, the erroneous development of a non-image forming area by applying a bias potential selected according to a background charge potential region to a second developing device. SOLUTION: The bias voltage applied to a first developing device 24 is strictly defined to control the development of a background and an image. The developing bias of the next developing device 34 is increased to prevent the overplating and for maintaining development processing for the corresponding color image, the increase of a voltage for forming a related image is required as well. For instance, the developing bias applied to the developing device 24 is lower than that applied to the developing device 34. The developing bias for a fixed developing device is selected and controlled to be substantially equal to or a little higher than a background voltage produced by the cycle of development, reelectrification and the formation of the image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates generally to electrostatographic printing apparatuses, and more particularly, to the development of a background charge potential area on an imaging member to prevent development of the image on the imaging member during subsequent image development processing. That is, it relates to an image-on-image multi-color printing apparatus which selectively and systematically adjusts individual imaging and developing bias voltages as a function of non-uniform background charge potential.

[0002]

2. Description of the Related Art In order to generate a multi-color output image,
Electrostatographic printing devices generally use so-called subtractive color mixing. Multi-color images are created by subtractive color mixing from three colors: cyan, magenta, and yellow. Cyan, magenta, and yellow are complementary colors of the three primary colors having light sequentially absorbed from white light. In the case of an electrostatographic printing apparatus, various methods can be used to produce a full color image using cyan, magenta and yellow toner images.

One typical method of producing a multicolor image of particular interest to the present invention is known as the Recharge, Expose and Development (REaD) image-on-image method. Have been. The method includes the steps of producing a developed multi-layer composite multi-color image by using a photoconductive surface (or another recording medium).
It is necessary to deposit different color toner layers on top of each other. In this method, first the first
A first latent image corresponding to the subtractive primary color of the developer of the developing device is recorded on a recording medium and developed. Thereafter, the recording medium having the developed first image is recharged, and a second latent image corresponding to another subtractive primary color is developed into the developed first latent image.
It is re-exposed to record on the image and is developed again with a second developer of the appropriate color. This process is repeated until all the different colored developer layers are correctly superimposed and deposited on the recording medium. This multilayer composite image is then transferred from the surface of the recording medium to a copy sheet or other support and fixed to produce a multi-color print output. A first latent image is generated and developed, and then an additional latent image is generated on top of the developed first image and developed to superimpose a plurality of developed images on each other. Various variants are known in the art, and the invention can be used to advantage. For example,
The ionographic printing method does not require a uniform charging or recharging of the recording medium, but instead, because the ionographic writing head sprays ions onto the recording medium in the form of an image to produce an image, which is The REaD method can be modified by performing the image forming / developing process as described above. One commercially available example of such a device is equipped on a Xerox 8900 series printing device.

[0004] As an example, the REaD color processing described above can be embodied in one of two architectures using typical electrostatographic printing methods. (1) In the case of a single-pass / single-transfer architecture, a plurality of image forming units each including a charging device, an image forming device, and a developing device are configured as one photoconductive belt (or Drum). (2) In the case of the multi-pass / single-transfer architecture, an image forming unit including a charging device, an image forming device, and a plurality of developing devices is disposed around a photoconductive belt or a drum. As the name implies, 1
Multi-pass architectures only rotate the photoconductive belt or drum once to produce a color image, while multi-pass architectures produce photoconductive belts to produce color prints or copies. Alternatively, the drum needs to be rotated several times. Various other methods and devices (each color separation is imaged and developed in turn, so each developing station (except for the first developing station) is an electrostatic latent image on the area where the previous latent image was developed) Has to be applied to the developer) and has been successfully implemented.

[0005] One important problem that arises in systems where successive developments are performed on previously developed images to produce a multi-color image is that the surface charge of a latent image can be reduced during the corresponding development cycle. That is, the toner particles may not be completely neutralized by the toner particles attached to the image. CAD
In the case of ionography, if an electrostatic latent image of one color separation is not completely discharged by toner particles during a development cycle, the electrostatic latent image may attract another color of toner in the next development step. There is. Similarly, in the case of the REaD method, in the processing step of recharging the surface of the photoconductor in preparation for the next image forming cycle, since a previously developed image is present, this recharging step is performed on the photoconductor. May generate a non-uniform charge potential. This non-uniform charge potential results in a non-uniform background potential, which will be developed in the next development step. Similarly, the exposing and / or imaging steps may cause the recording medium to discharge non-uniformly, creating a non-uniform background charge potential, which may be incorrectly developed in the next development step. There will be.

Therefore, in the case of the image-on-image electrostatographic printing method, various things may occur. After the previous development step, a residual charge potential may remain on the recording medium, ie a non-uniform background potential may develop, which will be developed in another color in the next development step. The phenomenon that the color of the second process incorrectly develops non-imaging areas in the area that must not be developed in that process step is a phenomenon that is overplating.
Also known as image staining. See RM Schaffert, E
lectrophotograthy (London: Focal Press, 1975), pp.
See 184-186.

[0007]

Many schemes have been pursued to solve the problem of overplating. For example, US Pat. No. 4,701,387 discusses the problem of developing residual images and proposes a solution in which after each development step the developed surface is rinsed with a polar rinse. It has been suggested that the application of the polar rinsing liquid neutralizes and decomposes residual reverse ions coming out of the charge control agent and the stabilizer present in the liquid developer.
While the method of U.S. Pat. No. 4,701,387 may be effective in resolving the problem of image staining, such multiple cleaning procedures are time consuming and would not be acceptable.

[0008] The present invention provides a method for controlling overbias by controlling the bias voltage applied during the imaging and / or development steps of a typical electrostatographic printing method to substantially prevent overplating. That is, an apparatus and a method for removing image staining are considered. Thus, the present invention is directed to a multi-color printing apparatus in which the defined color image forming and developing bias is determined by the performance of the previous color developing and / or recharging and / or image forming steps. Disclosed is a scheme for selectively controlling a bias voltage applied to each individual image forming / developing device present therein as a function of a characteristic related to a residual image on a recording medium, ie, a residual voltage.

[0009]

SUMMARY OF THE INVENTION As a first aspect, the present invention provides an electrostatographic printing apparatus for generating a multi-color output image from an input image signal. The printing apparatus includes: (a) a recording medium configured to record thereon a plurality of electrostatic latent images defined by an image charge potential area and a background charge potential area; and (b) an input image signal. Means for generating a first electrostatic latent image corresponding to the first color separation on a recording medium;
(C) developing the first electrostatic latent image on the recording medium with a developer,
(E) means for generating a first image; (d) means for generating a second electrostatic latent image corresponding to the second color separation of the input image signal by superimposing the second electrostatic latent image on the developed first image on the recording medium; A) developing the second electrostatic latent image on the recording medium with a developer to generate a second image; and (f) generating a second image to substantially prevent development of the residual image; In the developing step, there is provided a means for selectively applying a bias voltage as a function of a background image potential area on the recording medium.

According to a second aspect of the present invention, there is provided an electrostatographic printing method for generating a multi-color output image from an input image signal. The method includes: (a) preparing a recording medium configured to record a plurality of electrostatic latent images; and (b) forming a first electrostatic latent image corresponding to a first color separation of an input image signal. Generating on a recording medium; (c) developing a first electrostatic latent image on the recording medium with a developer to generate a first image; (d)
Generating a second electrostatic latent image corresponding to the second color separation of the input image signal on the developed first image on the recording medium; and (e) generating the second electrostatic latent image on the recording medium. With a developer to generate a second image, and (f) generating and / or developing a second image to substantially prevent development of a background image potential area on the recording medium. In the process,
Applying a selective bias voltage as a function of the background image potential region.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS To facilitate a general understanding of the present invention, a description will be given with reference to the drawings, in which the same components are denoted by the same reference numerals. FIG. 1 is a schematic front view of a typical full color electrostatographic printing apparatus incorporating features of the present invention. Since the art of electrostatographic printing is well known, the various processing units used in the printing apparatus of FIG. 1 will be briefly described before describing the present invention in detail. It will be apparent from the following description that the apparatus of the present invention can be successfully adapted and used in a wide variety of printing devices, and its use is not necessarily limited to the particular electrostatographic printing devices described herein. There will be. For example, it is clearly understood that the method and apparatus of the present invention can be applied to powder or liquid ionographic printing devices as well as powder toner type electrostatographic printing devices and liquid developer type electrostatographic printing devices. Will be. Hereinafter, the present invention will be described with reference to its preferred embodiments, but it will be understood that it is not intended to limit the invention to these preferred embodiments. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalents, which are included within the spirit and scope of the claimed invention.

FIG. 1 illustrates a multicolor electrostatographic printing apparatus incorporating features of the present invention. The printing apparatus uses a multi-layer photosensitive belt 18 that includes a photoconductive surface deposited on a grounded conductive substrate. Preferably, the photoconductive surface is made of a selenium alloy and the conductive substrate is made of an aluminum alloy. The photosensitive belt 18 is rotated along a curved path formed by the rollers 12 and 14 to advance a continuous portion of the photosensitive belt and sequentially pass through various processing units disposed around the belt moving path. Roller 12 is rotationally driven in the direction of arrow 13 by a suitable motor and transmission (not shown), and roller 14 is similarly rotated in the direction of arrow 13 to advance belt 18 in the direction of arrow 16. preferable.

First, the belt 18 passes through the charging section.
In the charging section, corona generator 20 deposits charge on the photoconductive surface of belt 18 to charge it to a relatively high, substantially uniform potential.

After a substantially uniform charge has been placed on the photoconductive surface of belt 18, electrostatographic printing is accomplished by imaging the input document (or by providing a computer generated image exposure signal). ) Discharging the photoconductive surface into the shape of the image according to the output image to be generated; In this processing step, the charge previously placed on the photoreceptor is selectively discharged to form an electrostatic latent image corresponding to a desired output image.
This imaging process can be performed by a variety of techniques, but most often involves projecting the reflected light image onto a photoreceptor to discharge non-image areas, or by exposing the photoreceptor according to a computer-generated modulation signal. Implemented by selective exposure to a light source.

In the case of multicolor printing or copying, the image forming process must separate the image forming information into three primary colors to obtain a series of subtractive color image forming signals. Each individual image forming signal is proportional to the intensity of the incident light of each primary color. These image forming signals are transmitted to a series of individual image forming devices 22, 32, 4
2,52. These image forming devices 22, 32,
42 and 52 may be equipped with a raster output scanner (ROS) or an LED array to generate an electrostatic latent image of a complementary color separation on the charged photosensitive belt 18. Generally, each of the image forming apparatuses 22, 32, 42, and 52 writes latent image information one pixel at a time.

In the case of the typical electrostatographic system shown in FIG. 1, the electrostatic latent images of each color separation are supplied to the donor roll developing devices 24, 34, 4
4, 54 continuously develop on the photosensitive belt 18. Each developing device carries a developer of a different color to contact the electrostatic latent image on the photoreceptor surface, and develops the latent image with colored toner particles to generate a visible image. By way of example, developing device 24 carries a cyan colored developer, developing device 34 carries a magenta colored developer, developing device 44 carries a yellow colored developer, and developing device 54 carries a black developer. Each different color developer contains colored toner particles. The toner particles are charged to a polarity opposite that of the latent image on the photoconductive surface of belt 18 such that the toner particles are attracted to the electrostatic latent image to produce a visible image.

In a typical donor roll developing device, the donor rolls 25, 35, 45, 55 are coated with a layer of an appropriately colored developer to form a belt 18 on which a latent image is formed.
Is rotated to carry the developer to the surface. The donor roll is generally electrically biased to the appropriate size and polarity to promote attraction of the toner particles to the latent image and to prevent transfer of the toner particles to non-image areas. Each developing device 24, 34, 44, 54 is substantially identical to one another and represents one of a variety of known developing devices that can be used to apply developer to a photoconductive surface or any other type of recording medium. ing. It will also be appreciated that this detailed description is directed to a general description of a multi-color printing device that can incorporate the present invention. No. 5,570,173. Among the many additional subsystems described in the various patent literature and publications available, for example, US Pat.
It will be appreciated that additional subsystems may be provided, such as the image conditioning apparatus described in US Pat.

In a typical embodiment, the electrostatic latent image of the first color separation is developed in developing device 24 using a cyan developer. Thereafter, photosensitive belt 18 continues to move in the direction of arrow 16 and passes optional metering device 28. Metering device 28 can be provided to reduce the thickness of the developed image on the photoreceptor surface. Next, the developed image moves to the next charging station, where corona generator 30 recharges the photoreceptor to a substantially uniform charge potential. Next, the image forming device 32 selectively erases the electric charge placed by the corona generating device 30 and records an electrostatic latent image of the second color separation corresponding to the area developed with the magenta developer. This electrostatic latent image of the second color separation can be wholly or partially superimposed on the previously developed cyan image on the photoconductive surface of belt 18. This electrostatic latent image is advanced to the next developing device 34, where it is developed with magenta toner.

After the electrostatic latent image has been developed with magenta toner, the photoconductive surface of the belt 18 continues to move in the direction of arrow 16 and passes through the next metering device 38 to the corona generator 40.
Reach Corona generator 40 charges the photoconductive surface again to a substantially uniform potential. Next, the image forming device 42 selectively discharges the new charge potential on the photoconductive surface to record an electrostatic latent image of the third color separation. This electrostatic latent image developed with yellow toner can be fully or partially superimposed on the previous cyan and magenta images. In this manner, a yellow toner image is formed on the photoconductive surface of belt 18 in proper registration with the previously developed cyan and magenta images. It will be understood that the color of the toner particles in each developing device may be in a different arrangement and order than described herein.

Next, the belt 18 continues to move, passes through the next metering device 48, reaches the corona generating device 50, and then proceeds to the image forming device (ROS) 52, where the belt 18 is developed with black toner. Are selectively discharged. In one embodiment of this final black development step, the developed image is processed only on those portions of the photoconductive surface that are to be black in the printed page, by a process known as undercolor removal. Placed but not overlaid on the previously developed cyan, magenta and yellow images.

The last developed composite multicolor image is then advanced to the transfer station. In the transfer section, the stack 10
The copy sheet 100 (for example, paper or the like) sent from the second unit by the sending roll 104 is guided to the transfer unit by the chute 106. In the transfer section, the developed composite multicolor image on belt 18 is transferred to sheet 1
To attract to 00, corona generator 108 sprays ions on the back of sheet 100. Although an electrostatic transfer process has been described, it will be appreciated that a variety of other transfer methods are known, including mechanical and thermal activation, that can be used to perform the transfer in the apparatus described herein. Further, although a case has been described here in which the developed composite multicolor image is directly transferred to a sheet, the developed image is transferred to an intermediate member (for example, a belt or a drum) and then transferred to a copy sheet as is well known. ,
It will be appreciated that it can also take root. After the transfer, the conveyor belt 110 moves the copy sheet by the arrow 11
The sheet is conveyed to the fixing device in the direction of 2. The fixing device includes a heated fixing roll 114 and a pressure roll 116.
The two rolls 112 and 116 are elastically pressed against each other to form a nip through which the copy sheet passes. The fusing device acts to attach toner particles to the copy sheet to bond the multicolor image to the copy sheet. Finally, after fixing, the completed sheet is conveyed to the chute 120 by the conveyor 118, and the chute 12
0 guides the sheet to the catch tray 122 so that the operator can take it out.

In general, after the developed image has been transferred from belt 18, there is a tendency for undesired residual developer to remain on the surface of belt 18. For this reason, generally, the cleaning roller 60 made of a suitable synthetic resin rotates in contact with the belt surface in a direction opposite to the moving direction of the belt 18 to remove the residual developer. It will be appreciated that many photoconductive surface cleaning devices are known and any cleaning device is suitable for use with the present invention.

The above description is based on the intentional recharging of the photoconductive member, re-exposure of the charged photoconductive surface to record a latent image thereon, and subtraction of the latent image in a corresponding developing device. It is understood that the development is with one of the appropriate colored toner particles of the mixed primaries to be directed to a "REaD" process in which different color toner layers are superimposed on one another and deposited on the photoconductive surface of the belt 18. Will be done. It should be noted that either the well-known discharge area development (DAD) method for developing discharged portions or the charged area development (CAD) method for developing charged areas may be used.

It will further be noted that there are similar methods of making multicolor output prints in an electrostatographic manner. Of particular interest in connection with the present invention are the well-known ionographic printing methods for recording a latent image on a dielectric recording medium. A typical printing device of this type configured to produce a multi-color output print is shown in FIG.
Shown in It will be noted that the printing device of FIG. 2 is very similar to the printing device of FIG. 1 with two important exceptions. First, the recording medium embodied as the photoconductive belt 18 of FIG. 1 is an insulating or resistive dielectric belt (indicated by reference numeral 17 in FIG. 2) that can hold the applied charge. Has been replaced. In contrast to the photosensitive recording medium of FIG. 1, ionographic recording media generally have negligible, if any, photosensitivity. This is because the electrostatographic recording medium does not need to be kept in a light-tight environment, and is characterized by a low level of charge decay over time, which results in a substantially constant voltage profile of the recording medium. There are significant advantages, such as being.

A second feature of the ionographic electrostatographic printing apparatus is found in an image forming apparatus that produces a latent image on a recording medium 17. Once again, in contrast to the photosensitizing charging of the photoconductive recording medium and the subsequent selective discharge described with reference to FIG. 1, in an iocographic printing apparatus, the latent image transfers the charge onto the dielectric recording medium. It is formed by placing directly on the shape. In one simple form of ionographic imaging, a linear array of ion emitters,
That is, an electrostatic latent image is generated by placing the surface charges densely on the surface of the dielectric recording medium using an ion head. For example, US Pat. Nos. 4,042,939 and 4,311,
As disclosed in U.S. Patent No. 5,270, an aligned row of backup electrodes and an aligned row or more of writing needles supported in a dielectric support member facing the batch electrode. Various alternative imaging devices are known, such as write heads with electrodes.
It will be apparent to those skilled in the art that other electrode configurations for recording a latent image on a dielectric recording medium can be incorporated into the ionographic electrostatographic printing apparatus of FIG.

Therefore, the REaD described with reference to FIG.
As in the (recharge, exposure, and development) method, the ionographic electrostatographic printing apparatus of FIG.
A step of forming an electrostatic latent image on a recording medium in an image forming unit provided with 33, 43, or 53. Certain variations of the recording head include a plurality of recording (ie, writing) electrodes physically arranged to electrically address a dielectric surface of the recording medium as the recording medium moves past the image recording head. I have. Further, a series of backup electrodes are provided in line with the write electrode, and a print gap is formed between the backup electrode and the write electrode. As the potential difference between the addressed write electrode and the opposing backup electrode rises to a threshold level (also known as the passion breakdown point, which can be on the order of hundreds of volts), the electrostatic charge is reduced by the dielectric of the recording medium. Accumulates on body parts. As the dielectric recording medium moves past the image forming head, the timing of the energization of the electrodes selectively charges the dielectric recording medium to the shape of the image and forms the desired latent image.

After the latent image is formed on the dielectric recording medium 17, the electrostatic latent image is developed into a visible image by a developing process shown in FIG.
, Or at least similar to the development process described above. Similarly, the image transfer step and the fixing step can be performed using the method described above. Various apparatus and methods for performing the steps of an ionographic electrostatographic printing apparatus are known, and it will be apparent to those skilled in the art that any of them may be used.

As pointed out earlier, an important problem which exists in devices of the type which perform a subsequent development step on a previously developed image to produce a multicolor image is the incomplete erasure of image charge. When a developable charge potential arises due to the presence of a non-uniform background potential due to the presence of the developed image (which tends to increase the background potential), or when both occur Get up. These potentials can attract toner particles in the next development step, causing a phenomenon commonly known as "overplating" or "staining". This problem is caused by non-uniform background potential on the recording medium after development and / or recharging and / or imaging cycles (which may be developed in a different color in the next development step). Will be understood.

The present invention provides for image overplating or staining by deliberately choosing the development voltage bias in a manner that helps eliminate overplating events during each subsequent development cycle. A method and apparatus for preventing this is considered. Accordingly, the present invention provides for each individual color present in a multi-color printing device such that the determined color development bias is determined by the performance of previous color development and / or recharging and / or imaging steps. A plan is provided for applying a bias voltage to the developing device.

In its simplest form, the concept of the present invention is directed to applying a predetermined bias to each developing device to control development in a background area on the recording medium. For this reason, the bias of the developing roll is set to a voltage substantially equal to or higher than the charge potential in the background area. This biasing technique substantially prevents current developing devices from developing background areas (which may include some earlier image areas).

Changes in development due to changes in development bias can be compensated for in various ways. For example, a more sophisticated alternative embodiment of the concepts of the present invention has additional similar planned recharging bias voltages for each latent image generation step in a multi-color imaging process. Specifically, the latent image potential for any given color image generated on the recording member is selected to depend on the development bias of the previous color. In the preferred embodiment, both the image bias voltage and the development bias voltage are controlled according to the development parameters of the previous color of the multi-color process, effectively eliminating the problem of residual image overplating, thereby ensuring correct image area. Maintain development.

Next, the concept of the present invention will be described in terms of a typical bias voltage applied to each image forming and developing unit.
In the case of a basic developing device, the force applied to the toner particles is equal to the product of the electric charge and the electric field. Therefore, the basic rule that the toner particles are attracted to the recording medium only when the electrostatic force acting on the toner particles is greater than zero, It will be appreciated that the toner particles of the developer will follow. In a typical electrostatographic printing apparatus, a voltage bias is applied to the developing device (schematically shown in FIGS. 1 and 2), requiring a higher potential on the recording medium to attract toner particles from the developing device. It is. This fact is used to greatly reduce the amount of toner that develops the non-image areas, or background areas, of the recording medium. Therefore, a bias voltage is generally applied to the developing device to control background development.

From the above description, in the multicolor electrostatographic printing apparatus of the type described here, the bias voltage applied to the first developing device 24 for controlling the development of the background and the image is strictly determined. Will be recognized.

However, in accordance with the present invention, the bias voltage applied to the next developing device (in this case, developing device 34) is selectively controlled to prevent staining, ie, the overplating phenomenon. Next developing device 34
Since the development bias of the associated image is increased to prevent overplating, the imaging voltage of the associated image must be increased by substantially the same amount to maintain the development of the corresponding color image. By way of example, if there is no background potential on the imaging member, the typical imaging voltage of the second imaging device 32 or 33 can be about 100 volts and developed for the development of the second color. A bias voltage of 5 volts can be applied to device 34. However, if the first image development / recharging / imaging cycle leaves a background potential of 20 volts on the recording medium, in order to prevent the development of the residual image, the next developing device is used in accordance with the plan of the present invention. The applied bias voltage is raised to about 25 volts. To maintain the same voltage difference between the image and the corresponding developing device, the imaging or recharging voltage used to generate the second image must be increased as well. In this case, an electrical bias is applied to produce an image voltage of 120 volts on the second imaging device. The same scheme of increasing the voltage is such that the image voltage at the first image forming device 22 or 23 is lower than the image forming voltage at the second image forming device 32 or 33, and the image forming voltage at the second image forming device 32 or 33 is increased. The voltage is lower than the imaging voltage at the third imaging device 42 or 43, and the third imaging device 42 or 43
Will be applied to subsequent imaging and developing devices in the manner described above, such that the imaging voltage at is less than the voltage applied to the fourth imaging device 52 or 53.
Similarly, the developing bias applied to the developing device 24 is lower than the developing bias applied to the developing device 34, the developing bias applied to the developing device 34 is lower than the developing bias applied to the developing device 44, and The developing bias applied to the developing device 44 is lower than the developing bias applied to the developing device 54. Most importantly, the development bias at a given development device is selected and controlled to be substantially equal to or slightly greater than the background voltage generated by the development / recharge / imaging cycle. It is. The gradual increase of the image forming bias voltage and the developing bias voltage is a unique feature of the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic front view of a typical color electrostatographic printing apparatus incorporating an electrical bias scheme to prevent overplating or image staining in accordance with the present invention.

FIG. 2 is a schematic front view of a typical ionographic printing apparatus incorporating an electrical bias scheme to prevent overplating or image staining in accordance with the present invention.

[Explanation of symbols]

12, 14 roller 17 dielectric belt 18 photoreceptor belt 20, 30, 40, 50 charging section 22, 32, 42, 52 image forming apparatus (ROS, etc.) 23, 33, 43, 53 image forming apparatus (needle electrode recording Head, etc.) 24, 34, 44, 54 Developing device 25, 35, 45, 55 Donor roll 28, 38, 48, 58 Metering device 60 Cleaning roll 100 Copy sheet 102 Sheet stack 104 Delivery roll 106 Chute 108 Corona generator 110 Conveyor belt 114 Fixing roll 116 Pressure roll 118 Conveyor 120 Chute 122 Catch / Tray

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor David H. Pan, New York, United States of America 14625 Rochester Westfield, Co. Mons 10 (72) Inventor John F. Knapp United States of America, New York 14450 Fairport Lambeth Loop 38 (72) Inventor George A. Gibson 14450 Fairport Breezewood Court, New York, USA 1 (72) Inventor Robert M. Seams 95037, California, United States Santa Clara Fontaine Oaks 2780

Claims (2)

[Claims] 1. An electrophotographic printing apparatus for generating a multicolor output image from an input image signal, wherein a plurality of electrostatic latent images formed by an image charge potential area and a background charge potential area are recorded thereon. A first image forming apparatus that generates a first electrostatic latent image corresponding to a first color separation of an input image signal on the recording medium; and a first image forming apparatus on the recording medium. A first developing device that develops the electrostatic latent image with a developer to generate a developed first image; and a second electrostatic latent image corresponding to a second color separation of an input image signal on the recording medium. A second image forming apparatus that generates the second electrostatic latent image on the recording medium with a developer to generate a developed second image; A developing device; and a background charge potential region for substantially preventing development of the background charge potential region on the recording medium. Means for applying a bias potential selected in accordance with the above to the second developing device. 2. An electrostatographic printing method for generating a multicolor output image from an input image signal, wherein a plurality of electrostatic latent images formed by an image charge potential area and a background charge potential area are recorded thereon. Preparing a recording medium configured to perform the following steps: generating a first electrostatic latent image corresponding to a first color separation of an input image signal on the recording medium; Developing the electrostatic latent image with a developer to generate a developed first image; and developing the second electrostatic latent image corresponding to the second color separation of the input image signal on the recording medium. Generating a superimposed superimposed image on the first image; developing a second electrostatic latent image on the recording medium with a developer to generate a developed second image; In order to substantially prevent development of the background image potential area, the image generation step and Applying a selected bias voltage as a function of the background charge potential area on the recording medium during the developing step.